Core-needle biopsy versus repeat fine-needle aspiration for thyroid nodules initially read as atypia/follicular lesion of undetermined significance

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1 ORIGINAL ARTICLE Core-needle biopsy versus repeat fine-needle aspiration for thyroid nodules initially read as atypia/follicular lesion of undetermined significance Young Jun Choi, MD, 1 Jung Hwan Baek, MD, PhD, 1 * Chong Hyun Suh, MD, 1 Woo Hyun Shim, PhD, 1 Boseul Jeong, MD, 1 Jae Kyun Kim, MD, PhD, 2 Dong Eun Song, MD, PhD, 3 Tae Yong Kim, MD, PhD, 4 Ki-Wook Chung, MD, PhD, 5 Jeong Hyun Lee, MD, PhD 1 1 Department of Radiology, Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Songpa-Gu, Seoul, Korea, 2 Department of Radiology, Chung-Ang University College of Medicine, Dongjak-gu, Seoul, Korea, 3 Department of Pathology, University of Ulsan College of Medicine, Asan Medical Center, Songpa-Gu, Seoul, Korea, 4 Department of Endocrinology and Metabolism, University of Ulsan College of Medicine, Asan Medical Center, Songpa-Gu, Seoul, Korea, 5 Department of Surgery, University of Ulsan College of Medicine, Asan Medical Center, Songpa-Gu, Seoul, Korea. Accepted 12 August 2016 Published online 5 October 2016 in Wiley Online Library (wileyonlinelibrary.com). DOI /hed ABSTRACT: Background. The purpose of this study was to evaluate the role of core-needle biopsy (CNB) by comparing the results of CNB and repeat fine-needle aspiration (FNA) for thyroid nodules that are initially read as atypia/follicular lesion of undetermined significance (AUS/FLUS) on FNA. Methods. Among 2631 initial AUS/FLUS FNA results, 505 consecutive nodules (295 repeat FNAs and 210 CNBs) were retrospectively analyzed. The primary outcome was inconclusive (ie, nondiagnostic or AUS/FLUS). The secondary outcomes included inconclusive results of the subcategory, risk factors for inconclusive results, and diagnostic performance. Results. CNB demonstrated significantly fewer inconclusive results than repeat FNA for the overall nodules (40.9% vs 63%; p <.001). Repeat FNA and group FLUS were significant risk factors for inconclusive results (odds ratio ; p and odds ratio ; p <.001, respectively). All diagnostic performances using CNB were higher than repeat FNAs. Conclusion. CNB is more useful than repeat FNAs for reducing inconclusive results and improving the diagnostic performance of thyroid nodules with initial AUS/FLUS FNA results. VC 2016 Wiley Periodicals, Inc. Head Neck 39: , 2017 KEY WORDS: core-needle biopsy, atypia of undetermined significance, follicular lesion of undetermined significance, ultrasound, fine-needle aspiration INTRODUCTION The Bethesda System for Reporting Thyroid Cytopathology recommends using repeat fine-needle aspiration (FNA) for thyroid nodules that are initially diagnosed as atypia/ follicular lesion of undetermined significance (AUS/ FLUS). 1 However, the role of repeat FNA for AUS/FLUS nodules is controversial because repeat FNA also reproduces a significant number of repeat AUS/FLUS results (estimated up to 67%) Most patients with repeat AUS/FLUS results are referred for diagnostic surgery, and the majority of these patients are diagnosed with benign disease Thyroid surgery for these patients is controversial, and it exposes them to a 2% to 10% risk of serious surgical complications, including vocal cord paresis and hypoparathyrodisim. 14,15 In addition, the malignancy risks for this category demonstrate a broad range, reportedly 6% to 96.7%, and management plans vary among reports and institutions. 2,16 To overcome these limitations, several solutions, such as molecular *Corresponding author: J. H. Baek, Department of Radiology, Research Institute of Radiology, University of Ulsan College of Medicine, Asan Medical Center, 86 Asanbyeongwon-Gil, Songpa-Gu, Seoul , Republic of Korea. radbaek@naver.com analysis, 4,17 19 ultrasound images, and core-needle biopsy (CNB) have been suggested. CNB has been suggested as an alternative approach for collecting samples for thyroid nodule evaluation because it is known to be safe, and well-tolerated and demonstrates a low incidence of complications However, CNB may not always be technically feasible and requires more clinical experience for thyroid intervention. 32 Several recent studies have reported that CNB may be an accurate complementary test for thyroid lesions with prior AUS/FLUS FNA results Although these studies suggest the potential utility of using CNB to manage AUS/ FLUS or indeterminate nodules, the number of cases included in those reports was relatively small (maximum number of cases 5 191), and there is insufficient evidence for comparison to FNA. Therefore, the purpose of our present study was to determine the role of CNB by comparing it to repeat FNAs for thyroid nodules with initial AUS/FLUS FNA results in a large patient population. MATERIALS AND METHODS This retrospective analysis was approved by the Institutional Review Board of Asan Medical Center, and informed consent was waived for data evaluation. Written informed consent for routine thyroid ultrasound and HEAD & NECK DOI /HED FEBRUARY

2 CHOI ET AL. FIGURE 1. Diagram of the study population and final diagnoses. ultrasound-guided biopsy procedures was obtained from all patients before each ultrasound examination. Study population Between October 2008 and July 2013, 19,403 initial ultrasound-guided thyroid FNAs for thyroid nodules were performed at our institution, and the cytological results of 2631 (13.6%) procedures were AUS/FLUS. Among these 2631 procedures with initial AUS/FLUS FNA results, there were 210 CNB procedures and 295 consecutive repeat FNA procedures after obtaining the initial AUS/ FLUS FNA results in our analysis. The study included 107 men (mean age, 56.5 years; age range, years) and 398 women (mean age, 55.2 years; age range, years) with a mean age of 55.5 years (age range, years). A final diagnosis was made for 246 of the 505 thyroid nodules. A final malignant diagnosis was made when the malignancy was confirmed on the surgical specimen (n 5 87; 35.4%) or by CNB histology (n 5 14; 5.7%). A final diagnosis of a benign nodule was made when any one of the following criteria was met: (1) confirmation using a surgical specimen (n 5 28; 11.4%); (2) benign cytology findings confirmed at least twice on repeat follow-up FNA and/or CNB procedures (n 5 4; 1.6%); or (3) benign follow-up CNB or FNA readings and stable size during the 1-year follow-up period (n 5 113; 45.9%; see Figure 1). Ultrasound-guided fine-needle aspiration and coreneedle biopsy procedures Ultrasound examinations were performed using 1 of 4 ultrasound systems: iu22 or HDI 5000 unit (Philips Healthcare, Bothell, WA); Aixplorer ultrasound system (SuperSonic Imagine, Aix en Provence, France); or EUB unit (Hitachi Medical Systems, Tokyo, Japan) equipped with a linear high-frequency probe. In all cases, comprehensive ultrasound evaluations of the neck and thyroid gland were performed, and the size, location, and ultrasound findings were evaluated. The FNA and CNB procedures were performed by radiologists under the supervision of 3 clinically experienced thyroid radiologists (J.H.B., J.H.L., and Y.J.C.) with 18, 13, and 6 years of thyroid ultrasound experience, respectively. Either ultrasound-guided FNA or CNB was utilized based on the referring physician s preference or ultrasound operator s decision. For FNA, a 23-gauge needle was routinely used. Either the capillary or aspiration technique was used according to the characteristics of each nodule. 33 Direct smears were made in all cases, and all smears were immediately fixed with alcohol after FNA and were stained with Papanicolaou. Additional FNAs were recommended in the case of insufficient biopsy material by visual assessment. 34 For CNB, the biopsy procedures were performed using a 1.1-cm or 1.6-cm excursion, 18-gauge, double-action, spring-activated needle (TSK Ace-cut; Create Medic, Yokohama, Japan). Before inserting the core needle, we measured the longest diameter of the nodule and used power Doppler ultrasound to evaluate the vessels along the approach route in order to avoid hemorrhage. After induction of local anesthesia using 1% lidocaine at the needle puncture site, the end of the biopsy needle was advanced into the solid part of the nodule using a freehand technique. 27,34 After the tip of the biopsy needle had been advanced into the edge of the nodule, we reevaluated the vessels around the nodule in order to minimize vessel injury. After measuring the distance of fire (1.1 or 1.6 cm), the stylet and cutting cannula of the needle were sequentially fired. Tissue cores were placed in 10% buffered formalin immediately after the procedure and then conventionally processed. Additional CNB procedures were performed when the lesion was considered inaccurately targeted (as was the case for small nodules), or when an insufficient specimen was suspected on visual inspection. After biopsy, each patient was observed using firm local compression of the biopsy site for 10 to 20 minutes. When the patient complained of pain or swelling of the neck, repeat ultrasound examination was performed to evaluate complications. Cytohistological analysis FNA cytology and CNB histology specimens were reviewed by an experienced pathologist. FNA cytology diagnoses were categorized into 6 categories according to the Bethesda System for Reporting Thyroid Cytopathology as follows: nondiagnostic; benign; AUS/FLUS; follicular neoplasm/suspicious for a follicular neoplasm (FN/ SFN); suspicious for malignancy; and malignant. 1 Because the diagnostic criteria for CNB have not been standardized for thyroid nodules, in this study, CNB histological diagnoses were categorized into the same 6 categories as the Bethesda System for Reporting Thyroid Cytopathology according to the histopathological CNB results. 26,27,34,35 A nondiagnostic CNB reading included the absence of any identifiable follicular thyroid tissue, the presence of only normal thyroid gland tissue, or tissue containing only a few follicular cells insufficient for diagnosis. The benign CNB findings included colloid nodules, nodular hyperplasia, and lymphocytic thyroiditis. AUS/ FLUS on CNB included nodules in which some atypical cells were present but were not diagnostic of suspicious malignancy or malignant tumor, and included cellular 362 HEAD & NECK DOI /HED FEBRUARY 2017

3 CORE-NEEDLE BIOPSY VERSUS REPEAT FNA FOR ATYPIA/FOLLICULAR LESION OF UNDETERMINED SIGNIFICANCE follicular nodules in which the distinction between a follicular neoplasm and hypercellular hyperplastic nodule was not possible. FN/SFN on CNB included nodules with histological features favoring follicular neoplasm. Suspicious-for-malignancy on CNB was considered when the specimen demonstrated atypia but there was insufficient evidence for a definite diagnosis of malignancy. A malignant reading on CNB was considered when the specimen unequivocally demonstrated the features of cancer. Cases of AUS/FLUS were subclassified according to the morphologic features noted in the cytopathology report. 10,27,36,37 Group AUS was used for cases that demonstrated nuclear atypia, such as the presence of occasional nuclear grooves, abnormal chromatin patterns, or nuclear overlapping and crowding, those being anomalous findings within individual cells. These findings raised concern for papillary thyroid carcinoma. Group FLUS was used for cases that demonstrated low cellularity with a predominantly microfollicular pattern and no or minimal colloids, which are a concern for follicular neoplasm. Analysis of the ultrasound findings The ultrasound images were independently and retrospectively reviewed by 2 radiologists (J.H.B. and Y.J.C.). Neither reviewer had any information regarding a patient s clinical history, previous imaging results, or histologic results. Any diagnostic discrepancies between the 2 reviewers were resolved by consensus. The ultrasound findings of the nodules were evaluated for the following features: size (maximum diameter); composition (solid, predominantly solid, predominantly cystic, or cystic); shape (oval-to-round, irregular, or taller-than-wide); margins (well-defined, ill-defined, or spiculated); echogenicity (hyperechoic, isoechoic, hypoechoic, or marked hypoechoic); presence of echogenic dots suggestive of microcalcifications; and the presence of macrocalcifications. 38,39 The ultrasound criteria for malignant nodules included taller-than-wide shape, spiculated margin, marked hypoechogenicity, and the presence of microcalcifications Outcome measures The primary study outcomes included inconclusive results for the overall nodules and nodules >1 cm across the maximum diameter. An inconclusive diagnosis was defined as repeat FNA or CNB results showing nondiagnostic or AUS/FLUS results. The secondary outcome measures included inconclusive results in the subcategory of group AUS and group FLUS, risk factors for inconclusive results, overall diagnostic performance for the diagnosis of thyroid malignancy, and malignancy risk in the group AUS and group FLUS with adjunctive, malignant ultrasound findings. Data and statistical analysis The data are presented as the means and SDs for continuous variables, and as the number of patients for categorical variables. The Student s t test was used to analyze the differences in continuous variables (ie, patient age and nodule size). The Fisher s exact test was used to compare categorical variables: the inconclusive results; the 6 categories of the Bethesda System; patient sex; nodule features on ultrasound; and final malignant nodules. Estimates of the malignancy risk in thyroid nodules are subject to several biases because not all nodules undergo surgical resection or confirmatory diagnostic analysis. Therefore, we determined the conceivable ranges of the malignancy rates. The lower-bound estimate was calculated by dividing the number of confirmed malignancies by the total number of nodules. This lower-bound estimate assumed that nodules without a final diagnosis were benign. The upper-bound estimate was calculated by dividing the number of confirmed malignancies by the number of nodules with a final diagnosis. The true prevalence most likely lies between the lower-bound and upper-bound approximations. 3 To determine the independent risk factors associated with second inconclusive results, the results of the repeat FNA and CNB procedures after the initial AUS/FLUS FNA results were divided into 2 groups: conclusive and inconclusive. The parameters of the 2 groups were compared using univariate analysis, including the use of the Student s t tests to assess numeric values and the Fisher s exact test for categorical values. Subsequently, the parameters that were found to be significantly different were evaluated using multivariate logistic regression analysis in order to determine any independent risk factors. The sensitivity, specificity, positive predictive value, and negative predictive value of using repeat FNA and CNB to diagnose thyroid malignancy and overall diagnostic accuracy were calculated. All statistical analyses were performed using statistical software (MedCalc version 15.6; MedCalc Software, Mariakerke, Belgium; or SPSS version 19.0 for Windows, SPSS, Chicago, IL), and p values <.05 was considered statistically significant. RESULTS Demographic data Table 1 compares the demographic data of the patients assessed using repeat FNA and CNB. The mean size of the 505 nodules was 12.9 mm (range, 2 60 mm). Size, ultrasound features, final pathology of the nodule, and patient sex did not demonstrate a statistically significant difference (p >.05). The age of the patients who underwent repeat FNA was significantly older than the CNB patients (p 5.001). In total, 101 nodules received a final diagnosis of malignancy (89 classic-type papillary thyroid carcinomas; 9 follicular variant papillary thyroid carcinomas; 2 follicular carcinomas; and 1 H urthle cell carcinoma). Hence, the estimated risk of malignancy was between 20% (101 of 505) and 41.1% (101 of 246) (the denominators range from the total number of nodules [n 5 505] to the number of nodules that received a final diagnosis [n 5 246]). There were no major complications in either the repeat FNA or CNB groups, and no patients required hospital admission or intervention. There was no case of needle-track metastasis at follow-up. In 2 patients of FNA (0.6%) and 1 patient of CNB (0.4%), neck swelling and pain occurred because of the perithyroidal hematoma. These symptoms were relieved after manual compression for 1 hour. HEAD & NECK DOI /HED FEBRUARY

4 CHOI ET AL. TABLE 1. Demographic data for the study patients evaluated using repeat fine-needle aspiration and core-needle biopsy for thyroid nodules with initial atypia of undetermined significance/follicular lesion of undetermined significance fine-needle aspiration results. Repeat FNA (n 5 295) CNB (n 5 210) p value Age, y (29 81) (25 81).001 Sex, male/female 57/238 50/ Nodule size Maximum diameter, mm (2 49.9) (3 60).055 Nodule number 1 cm Ultrasound features Suspicious ultrasound features >.99 Macrocalcification 49 (16.6%) 44 (21%).244 Predominantly cystic 9 (3.1%) 6 (2.9%) >.99 Final malignant nodules, % Abbreviations: FNA, fine-needle aspiration; CNB, core-needle biopsy. The Student s t test was used to analyze the differences in patient age and nodule size. The Fisher s exact test was used to compare the other categorical variables. Data are means 6 standard deviations (range) for age and nodule size. Primary outcomes Inconclusive results among overall nodules and nodules >1 cm in diameter. Table 2 compares the diagnostic results obtained using repeat FNA and CNB to assess overall AUS/FLUS nodules and AUS/FLUS nodules >1 cm. The incidence of inconclusive results obtained using CNB was significantly lower than that obtained using repeat FNA among overall AUS/FLUS nodules (40.9% vs 63%; p <.001) and AUS/FLUS nodules >1 cm (45.9% vs 64.7%; p <.001). The incidence of nondiagnostic results using CNB was significantly lower than that obtained using repeat FNA among overall AUS/FLUS nodules (5.2% vs 21%; p <.001) and AUS/FLUS nodules >1 cm (1.7% vs 16.7%; p <.001). However, there were no statistical differences in the incidences of repeat AUS/FLUS between repeat FNA and CNB. CNB demonstrated a significantly higher incidence of FN/SFN results among overall AUS/FLUS nodules (6.2% vs 0.7%; p <.001) and AUS/FLUS nodules >1 cm (9.2% vs 0.7%; p <.001) and a higher incidence of malignant results among overall AUS/FLUS nodules (21.9% vs 8.5%; p <.001). There were no significant differences in the incidences of the other diagnostic categories between repeat FNA and CNB. Secondary outcomes Inconclusive results in the group AUS and group FLUS subcategories. Table 3 compares the inconclusive results in the group AUS and group FLUS. Overall, the incidence of inconclusive results obtained using CNB was significantly lower than that obtained using repeat FNA in group AUS (29.1% vs 45.2%; p 5.045) and group FLUS (49% vs 67.8%; p 5.001). Among nodules >1 cm, the incidence of inconclusive results obtained using CNB was significantly lower than that obtained using repeat FNA in group FLUS (49.4% vs 66.7%; p 5.019), however, there was no statistical difference in the inconclusive results between CNB and repeat FNA in group AUS (39.5% vs. 46.7%; p 5.763). Risk factors for inconclusive results Among the 505 thyroid nodules initially diagnosed as AUS/FLUS, an inconclusive result was obtained in 272 nodules on repeat FNA or CNB. The results of the univariate and multivariate logistic regression analyses for the risk factors associated with inconclusive results are listed in Table 4. There were 3 significant risk factors associated with inconclusive results by univariate analysis: (1) the subcategory of the initial FNA results (group TABLE 2. Comparison of repeat fine-needle aspiration and core-needle biopsy in the diagnosis of thyroid nodules with initial atypia of undetermined significance/follicular lesion of undetermined significance fine-needle aspiration results. All (n 5 505) >1cm(n 5 270) Diagnosis* (Bethesda system) Repeat FNA [no. (%)] (n 5 295) Repeat FNA [no. (%)] (n 5 210) p value (n 5 150) (n 5 120) p value Nondiagnostic (I) 62 (21) 11 (5.2) < (16.7) 2 (1.7) <.001 Benign (II) 74 (25.1) 59 (28.1) (61.1) 42 (35).358 AUS/FLUS (III) 124 (42) 75 (35.7) (48) 53 (44.2).542 FN/SFN (IV) 2 (0.7) 13 (6.2) < (0.7) 11 (9.2) <.001 Suspicious for malignancy (V) 8 (2.7) 6 (2.9) >.99 1 (0.7) 4 (3.3).175 Malignant (VI) 25 (8.5) 46 (21.9) < (4.7) 8 (6.7).595 Abbreviations: FNA, fine-needle aspiration; CNB, core-needle biopsy; AUS, atypia of undetermined significance; FLUS, follicular lesion of undetermined significance; FN, follicular neoplasm; SFN, suspicious for a follicular neoplasm. * Diagnosed according to 6 categories of The Bethesda System for Reporting Thyroid Cytology. Comparison of the diagnosis obtained using repeat FNA and CNB (Fisher s Exact test). 364 HEAD & NECK DOI /HED FEBRUARY 2017

5 CORE-NEEDLE BIOPSY VERSUS REPEAT FNA FOR ATYPIA/FOLLICULAR LESION OF UNDETERMINED SIGNIFICANCE TABLE 3. Comparison of inconclusive diagnoses between Group AUS and Group FLUS. Group AUS Group FLUS All (n 5 172) >1cm(n 5 58) All (n 5 333) >1cm(n 5 212) (n 5 77) p value* Repeat FNA [no. (%)] (n 5 135) (n 5 100) p value* Repeat FNA [no. (%)] (n 5 233) (n 5 43) p value* Repeat FNA [no. (%)] (n 5 15) (n 5 110) p value* Repeat FNA [no. (%)] (n 5 62) Nondiagnostic 11 (17.7) 5 (4.5) (33.3) 2 (4.7) (21.5) 2 (2) < (14.8) 0 (0) <.001 AUS/FLUS 17 (27.4) 27 (24.5) (13.3) 15 (34.9) (46.4) 47 (47) > (51.9) 38 (49.4).776 Inconclusive diagnosis 28 (45.2) 32 (29.1) (46.7) 17 (39.5) (67.8) 49 (49) (66.7) 38 (49.4).019 Abbreviations: FNA, fine-needle aspiration; CNB, core-needle biopsy. * Comparison of the diagnosis obtained using repeat FNA and CNB (Fisher s Exact Test). FLUS [p <.001]); (2) diagnostic method (repeat FNA [p <.001]); and (3) calcification (p 5.037). By multivariate logistic regression analysis, the subcategory of the initial FNA result (group FLUS [odds ratio ; p <.001]) and diagnostic method (repeat FNA [odds ratio ; p 5.001]) were independent risk factors associated with inconclusive results. Overall diagnostic performance for malignancy The diagnostic performances of repeat FNA and CNB and the final diagnoses (n 5 246) are summarized in Table 5. Final diagnoses were obtained in 117 of 295 nodules using repeat FNA and 129 of 210 nodules using CNB. All statistical measures for the diagnosis of malignancy, including sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy, were higher using CNB than repeat FNA. Malignancy risk of the group AUS and group FLUS with adjunctive, malignant ultrasound findings The overall estimates for malignancy risk in the group AUS and group FLUS ranged from 41.9% (72 of 172) to 66.1% (72 of 109) and from 8.7% (29 of 333) to 21.2% (29 of 137), respectively (the denominators range from the total number of nodules to the total number of nodules with a final diagnosis). Table 6 compares the risk of malignancy in patients with adjunctive malignant ultrasound findings in the group AUS and group FLUS patients. The estimate of malignancy risk ranged from 71.4% to 88.7% for thyroid nodules in the group AUS patients that had malignant ultrasound findings, although the estimate of malignancy risk ranged from 4.9% to 11.6% in group FLUS patients without malignant ultrasound findings. DISCUSSION In this study, we compared the role of CNB and repeat FNA to assess thyroid nodules that initially demonstrated AUS/FLUS results. We found from our analyses that the incidence of inconclusive results using CNB was significantly lower than that obtained using repeat FNA among patients with initial AUS/FLUS nodules (overall nodules, nodules >1 in diameter, and the subcategories for nuclear atypia [group AUS] or microfollicular architecture [group FLUS]). The independent risk factors for inconclusive diagnosis included the biopsy method (repeat FNA) and the subcategory of the initial diagnosis (group FLUS; microfollicular architecture). In addition, CNB demonstrated a higher diagnostic performance for malignancy than repeat FNA. Moreover, there were no major complications in either the repeat FNA or CNB. These results suggest that CNB, rather than repeat FNA, can be used as a subsequent diagnostic approach for assessing thyroid nodules with initially AUS/FLUS FNA results. The Bethesda System for Reporting Thyroid Cytopathology suggests that the AUS/FLUS category is an optional group for FNA readings that are not clearly benign, suspicious, or malignant and recommends repeat FNA as a management tool. 1 The 2015 American Thyroid Association management guidelines propose using repeat FNA or molecular testing after considering the clinical and HEAD & NECK DOI /HED FEBRUARY

6 CHOI ET AL. TABLE 4. Univariate and multivariate logistic regression analysis to determine the risk factors associated with inconclusive results. Conclusive [no. (%)] Inconclusive [no. (%)] p value, univariate Odds ratio (95% CI) p value, multivariate Age, y < (57.9) 177 (65.1) (42.1) 95 (34.9) Sex Male:female 54:179 53: Nodule size 1.0 cm 115 (49.4) 120 (44.1).239 >1 cm 118 (50.6) 156 (55.9) Initial FNA result Group AUS 107 (45.9) 65 (23.9) < ( ) <.001 Group FLUS 126 (54.1) 207 (76.1) Final diagnosis Benign 107 (56.6) 38 (66.7).176 Malignant 82 (43.4) 19 (33.3) Diagnostic method Repeat FNA 109 (46.8) 186 (68.4) < ( ).001 CNB 124 (53.2) 86 (31.6) Composition Solid 183 (78.5) 211 (77.6).794 Predominantly solid 41 (17.6) 55 (20.2).454 Predominantly cystic 9 (3.9) 6 (2.2).274 Cystic 0 (0) 0 (0) Shape Ovoid to round 203 (89.0) 239 (89.2).959 Irregular 25 (11.0) 29 (10.8) Orientation Parallel 198 (86.8) 242 (90.3).225 Nonparallel 30 (13.2) 26 (9.7) Margin Smooth 103 (45.2) 133 (49.8).303 Spiculated 34 (14.9) 29 (10.9).178 Ill-defined 91 (39.9) 105 (39.3).894 Echogenicity Isoechoic 110 (48.5) 121 (45.1).462 Hypoechoic 85 (37.4) 118 (44.0).138 Marked hypoechoic 29 (12.8) 25 (9.3).220 Hyperechoic 3 (1.3) 4 (1.5) Calcification None 157 (67.4) 206 (75.7) ( ).190 Macrocalcification 49 (21.0) 44 (16.2).161 Microcalcification 27 (11.6) 22 (8.1).185 Abbreviations: CI, confidence interval; FNA, fine-needle aspiration; CNB, core-needle biopsy. sonographic features. 43 However, repeat FNA does not seem to be a satisfactory solution because repeat FNA allows a significant proportion of persistent AUS/FLUS cases, inconclusive results, and demonstrates a high falsenegative rate Several molecular analyses in FNA have been suggested as adjunctive diagnostic tools for patients with AUS/FLUS thyroid nodules. The B-type Raf (BRAF) V600E and RAS mutations demonstrate high specificity and positive predictive values; however, they demonstrate limited sensitivity, a high false-negative rate, and a low negative predictive value for detecting thyroid cancer, so these analyses are insufficient for evaluating patients with AUS/FLUS thyroid nodules and avoiding diagnostic surgery. 4,17 19 A prospective study using a 7-gene mutation testing panel (BRAF, NRAS, HRAS, KRAS, RET/PTC1, RET/PTC3, and PAX8/PPARc) for nodules with an AUS/ FLUS cytology (653 consecutive nodules, of which 247 had surgical follow-up) reported a 63% sensitivity and 99% specificity for detecting thyroid malignancy. 44 In our present study, CNB showed an 81.7% sensitivity and 100% specificity for diagnosing thyroid malignancy. Recent studies have described the usefulness of gene-expression analyses, which demonstrated high sensitivity and negative predictive value for detecting thyroid cancer, and suggest consideration of a conservative approach for the benign cases according to gene-expression classifier results. 45,46 Labourier et al 47 have reported that multiplatform testing for DNA, mrna, and mirna also demonstrates high sensitivity and specificity for detecting thyroid cancer. The American Thyroid Association management guidelines and the American Association of Clinical Endocrinologists, Associazione Medici Endocrinologi, and European Thyroid Association guidelines suggest that ultrasound-guided CNB may offer additional information regarding thyroid nodules that demonstrate inadequate cytologic results on FNA. 43,48 Currently, there are no definite guidelines on how CNB 366 HEAD & NECK DOI /HED FEBRUARY 2017

7 CORE-NEEDLE BIOPSY VERSUS REPEAT FNA FOR ATYPIA/FOLLICULAR LESION OF UNDETERMINED SIGNIFICANCE TABLE 5. Diagnostic performance of repeat fine-needle aspiration and core-needle biopsy for thyroid nodules with initial atypia of undetermined significance/follicular lesion of undetermined significance findings. Repeat FNA (n 5 117) CNB (n 5 129) Diagnostic accuracy 87.2% (102/117) 91.5% (118/129) Sensitivity 65.8% (27/41) 81.7% (49/60) Specificity 98.7% (75/76) 100% (69/69) Positive predictive value 96.4% (27/28) 100% (49/49) Negative predictive value 84.3% (75/89) 86.3% (69/80) Abbreviations: FNA, fine-needle aspiration; CNB, core-needle biopsy. The gold standard for final diagnosis was the surgical specimen or CNB histology for malignant nodules, and surgical specimen or follow-up cytology or ultrasound for benign nodules. should be used to evaluate AUS/FLUS thyroid nodules. Recently, several previous studies have demonstrated that CNB is a valid approach for collecting samples for AUS/ FLUS thyroid nodule evaluation, as it is known to be safe, well-tolerated, and demonstrates a low incidence of complications A recent prospective study showed that CNB is more useful than repeat FNA for reducing the incidence of inconclusive results (26.7% vs. 49.1%) and improving sensitivity for thyroid malignancy (78.5% vs. 55.4%) for thyroid nodules with previous AUS/FLUS results. 26 Several retrospective studies also report that CNB demonstrates low inconclusive results and high sensitivity and specificity for thyroid cancer in patients with AUS/FLUS thyroid nodules. 27,49 51 Although these studies suggest the potential utility of using CNB to manage AUS/FLUS or indeterminate nodules, the number of cases included in these previous reports was relatively small (maximum number of cases 5 191) Our current and larger dataset (n 5 505) has reproduced the result of these previous studies: CNB reduced the incidence of inconclusive results and improved the diagnostic performance for malignancy over repeat FNA for thyroid nodules that initially demonstrated AUS/FLUS results on FNA. Based on these observations, we conclude that CNB can reduce the frequency of repeat FNA or unnecessary diagnostic surgery. The low incidence of inconclusive results and high diagnostic performance of CNB may be explained by several factors. First, CNB provides larger tissue samples; this may facilitate a more precise histological diagnosis than that offered by FNA and offers additional immunohistochemical staining for the differential diagnosis. 52 Applying molecular analysis to CNB specimens from thyroid nodules with prior indeterminate FNA results has been previously attempted. CNB diagnosed the majority of the previously identified indeterminate nodules, and the added immunohistochemical panel (galectin-3 plus HBME-1) showed increased sensitivity and specificity for malignancy diagnosis with CNB (from 79% to 100% and from 73% to 96%, respectively). 53 In addition, CNB plus BRAF V600E reduced inconclusive results in nodules with previous AUS/FLUS results. However, CNB plus BRAF V600E did not show significantly better diagnostic performance than CNB alone in thyroid nodules with previous AUS/FLUS results (accuracy: CNB, 93.1% vs CNB plus BRAF V600E, 94.3%). 49 Second, CNB provides more information about the histological architecture and relationship between the nodule and the adjacent thyroid tissue 26,29,50 ; this factor may also be a major cause for the higher rate of FN/SFN diagnosis using CNB noted in our present study. Third, CNB demonstrates less operator dependency if the needle successfully penetrates the nodule. 27,54 There have been several studies that identified the risk factors that affect nondiagnostic FNA results 55,56 and the risk factors associated with second nondiagnostic results. 34 However, there have been no previous reports on the risk factors associated with inconclusive results obtained using second ultrasound-guided biopsy to assess thyroid nodules with initial AUS/FLUS results. In our current study, the biopsy method (repeat FNA) and the subcategory of the initial diagnosis (group FLUS; microfollicular architecture) were significant risk factors that affected inconclusive results. A previous study also reported that the biopsy method (repeat FNA) is the most significant risk factor that affects the second nondiagnostic results. 34 Another previous study on using repeat FNA for prior AUS/FLUS results further reported a higher incidence of indeterminate diagnosis in the microfollicular architecture subcategory (11%) than in the nuclear atypia (2%) subcategory, 37 similar to our present study results. In our current study, the group FLUS was concerning for a follicular neoplasm, and the identification of a fibrous capsule separating the nodule from surrounding thyroid parenchyma is an important aspect of the differential diagnostic point between AUS/FLUS (especially in the group FLUS) and SFN/FN. 57 Even though CNB provides more information regarding the relationship between the nodule and adjacent thyroid tissue than FNA, 29 tissue sampling, including obtaining an adequate amount of fibrous capsule, might not be easy and confounds the diagnosis between benign hyperplastic nodules and follicular neoplasm. 52 Our present study had several limitations of note. First, this was a retrospective single center study, so some selection bias was inevitable. A small percentage of AUS/ FLUS category patients (505 of 2631) was enrolled, and TABLE 6. Malignancy risk for Group AUS and Group FLUS with adjunctive, malignant ultrasound findings. Combination of the cytological results with the ultrasound findings Final malignancies, no. of patients Malignancy risk Group AUS 1 ultrasound findings of malignancy % to 88.7% Group AUS 1 no ultrasound findings of malignancy % to 36.2% Group FLUS 1 ultrasound findings of malignancy % to 64% Group FLUS 1 no ultrasound findings of malignancy % to 11.6% Note: The malignancy risk 5 the number with a final diagnosis/number of combination of cytological results with the ultrasound findings. The denominators range from the total number of nodules to the number of nodules with a final diagnosis. HEAD & NECK DOI /HED FEBRUARY

8 CHOI ET AL. the rate of inconclusive results using repeat FNA and CNB was relatively high (53.9%). Hence, large-scale, prospective, multicenter studies are needed in the future to validate our present findings. Second, because many of the benign nodules were not confirmed by surgery, the number of thyroid nodules with a final diagnosis was limited. Third, the CNB results may have been influenced by the technique and experience of the operator or pathologist. Finally, 113 of 145 benign thyroid nodules (77.9%) were diagnosed based on benign follow-up CNB or FNA readings and stable size during the 1-year follow-up period, which could result in some malignant nodules being missed because the majority of papillary thyroid microcarcinomas behave in an indolent fashion and not increase in size over several-year follow-up. 58 In conclusion, CNB effectively reduces inconclusive results and improves diagnostic performance in patients with initial AUS/FLUS results on FNA. 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